1. Field of the Invention
The present invention concerns a heating apparatus for heating a fluid, in particular in domestic appliances, which comprises a tubular casing, at least one electrical resistance heating wire which is arranged in the interior of the tubular casing and which is embedded in an electrically insulating, heat-conducting insulating material in the tubular casing, at least one connection unit which is arranged in the interior of the tubular casing and which is passed outwardly out of the tubular casing for connection of the electrical resistance heating wire to an electrical energy source disposed outside the tubular casing, and at least one closure bead which closes the opening of the tubular casing.
2. Description of the Related Art
European patent application No 0 086 465 discloses a heating apparatus in the form of a tubular heater which is of the structure referred to hereinbefore. In that previously known heating apparatus, the connection unit is connected at its one end by way of a connecting pin to the electrical resistance heating wire. The other end of the connection unit projects out of the tubular casing of the previously known tubular heater and serves to connect the tubular heater to an electrical energy source. FIG. 1 shows a previously known heating apparatus of that kind.
As can be seen from FIG. 1 the region of the connection unit A, in particular the region of the overload safeguard means Ü is separated from the region of the electrical resistance heating wire W by a first disk SI1 of insulating resin. An insulating material IM is introduced into the region of the electrical resistance heating wire W. In comparison the major part of the connection unit A is enclosed by a plastic sleeve K which electrically insulates the connection unit A with respect to the tubular casing M. To connect the connecting pin AB to the overload safeguard means Ü a copper sleeve KH is pushed on to the end of the connecting pin A, that faces away from the interior of the tubular casing M. At its other end the copper sleeve KH is also pushed on to the thermal overload safeguard means Ü. Disposed in adjoining relationship therewith in the direction of the front end of the tubular casing M are two further material disks SI2, SI3 of insulating resin and an insulating bead IP.
That previously known heating apparatus suffers from a series of disadvantages: Thus, firstly a large number of individual parts are required in order to be able to arrange the connection unit in functionally secure and reliable relationship in the interior of the tubular casing. Due to that large number of parts but also due to the large number resulting therefrom of necessary handling operations for assembling that extensive number of components, the costs of the previously known heating apparatus are considerably increased. Furthermore the arrangement suffers from large tolerance additions. In addition after the insulating material has been introduced, for the purposes of compacting it, the tubular casing has to be reduced in size by way of reducing rollers from one diameter, for example 10 mm, to a reduced diameter, for example 8.5 mm. That can be effected both prior to assembly of the connection unit and also thereafter, in which respect in the latter case the reducing rollers must be lifted off the tubular casing in good time in order to avoid damaging the connection unit, in particular the thermal overload safeguard means. The reducing operation makes it necessary for the tubular casing of the heating apparatus to be subjected to a re-crystallization annealing operation as otherwise there is the danger that, in a process for bending the tubular casing in order to impart thereto for example a U-shaped or W-shaped configuration, the tubular casing would tear. Furthermore the heating apparatuses have to be insulated as otherwise the filling material will absorb moisture and thus a short-circuit can occur from the electrical resistance heating wire to the tubular casing.